Currently, storage apparatuses are utilized to store data. A storage apparatus includes a plurality of memory devices, such as hard disk drives (HDD) and solid state drives (SSD), to provide a large storage region. A storage apparatus is connected to a storage control apparatus that controls access to the memory devices for the purpose of data write and data read. A storage apparatus includes a storage control apparatus in some cases.
In the meantime, each memory device writes data into each unit (for example, physical sector unit) of a memory medium inside the memory device. When writing data that is smaller than a unit, each memory device executes what is called a read-modify-write process. Each memory device includes a cache for use in the read-modify-write process.
For example, the following procedure is performed to write data into a part of a physical sector. Each memory device reads all information of a target physical sector into a cache in the memory device (Read). The memory device modifies a modification target part of the information that is read into the cache (Modify). The memory device writes the modified information of the cache into the same physical sector (Write).
There is a proposal of an information processing apparatus that measures a read-modify-write processing speed of a host control unit and a read-modify-write processing speed of a media control unit and selects the unit having a higher processing speed to execute a read-modify-write process in the selected unit.
Also, there is a proposal in which a selection condition is detected from input/output (I/O) requests from a host computer, and an optimal processing method is selected and executed from among a plurality of read-modify-write processing methods on the basis of the selection condition.
See, for example, Japanese Laid-open Patent Publication Nos. 2010-33396 and 6-75709.
It is concerned that the time that it takes for a memory device to respond to a write process increases, when a free space of a cache becomes insufficient for read-modify-write processing by the memory device. Thus, a problem lies in how to change a read-modify-write executor from a memory device to a storage control apparatus, before the response performance of the memory device deteriorates.
For example, one can conceive of acquiring information of a used space of a cache in a memory device from the memory device in order to monitor the used space and detect a sign indicating deterioration of response performance due to insufficiency of a free space of the cache. However, the implementation method of a cache mechanism varies depending on vendors, and in addition its information is not disclosed in many cases, and thus it is difficult to monitor the used space of the cache directly from outside.